Fuse



A ril 22,1941. 0. H. JUNG ETAL FUSE Filed. Jan. 5, 1938 2 Sheets-Sheet lrlllrlllli l HHUHHHHHHHIHI lie ferrule 4 by a drop of solder 82. Theopposite end of the link, which projects into the thimble through theslot I 3, is embedded in a batch of fusible alloy ll of a lower meltingpoint than that of the fuse link II. The alloy H is carried by a thermalcon IS, the lower end of which projects into the cup rivet l0, and iselectrically secured thereto by means of solder or other suitablematerial l6, preferably having a higher melting point than the alloy ll.

Positioned under the link I! is a flat spring ll provided at one endwith an offset nose l8, which bears against the fuse link adjacent itsconnection with the thermal coil IS. The opposite end of the spring llextends between the walls of the sleeve 2 and thimble 3 adjacent thelink H. In carrying out the principles of the present invention, a discis of substantially the same diameter as the interior of, the thimble 3is positioned on the link adjacent its connection with the thermal coilI5, thus forming a shield between the link and coil, and also serving tocreate a compression chamber to within the thimble 3, as well as servingto aline and hold the thermal coil in central position out of contactwith the inner wall of the thimble.

That end of the link extending between the telescoped walls of thesleeve 2 and the thimble 3 is provided with an insulating wrapping orcover M, which extends at 22 to provide a complete insulation betweenthe fuse link i i and spring ill.

Figure 3 illustrates the present invention applied to a conventionaltype of one-piece plug, provided with a body 2| formed of moulded insulating material, and in which the link it extends through an opening 26formed in the body. The link is electrically connected to the metallicferrule or contact 25 by solder 26. Above the solder the linkissurrounded by suitable insulating material 24' poured into the opening24. in this form of the invention one end of the hat spring l'l extendsinto a recess 2? formed in the casing 23 adjacent the opening 24. Anotch or groove 28 is formed in the inner wall of the casingoppocartridge type iuse, comprising a casing 3i formed of insulatingmaterial, and provided with metallic end caps 32, which serve ascontacts for reception in a conventional fuse clip. The thermal coil iis soldered or otherwise electrically connected to one of the caps 32,while the fuse link ii is connected to the opposite cap. A contractilecoil spring 33, connected to the link M adjacent its restrictedpotential fusing portion, and to the cap 32 with which the opposite endof the link is secured, serves to space the severed ends of the linkupon fusing, as will be later described.

Considering now the operation ofthe present invention, with particularreference to that formdisclosed in Figures 1 and 2, upon conditions ofinitial overload to which circuits are subjected upon the starting of amotor, or other electrical appliances, the link ii is prevented fromblowing, in that it is proportioned to fuse within the range ofapproximately five times the full load rating of the device in thecircuit, and upward to and including short circuit conditions. In theevent of overloads below the foregoing values, the fusible alloy l4softens and allows the spring ll to'withdraw the end of the fuse stripfrom the alloy, thus opening the circuit. When a short circuit occurs,the fuse element H, which is heavy enough to withstand starting currentsor harmless overloads, will open in the manner described, and possiblyin other exposed portions between the disc l9 and the insulating wrapper2|. At the same time, the disc is will obstruct any tendency of the arcto burn upwardly on the link, and should the fusing occur in the linkabove the disc,- as upon short circuit or heavy overloads, the latteraffords protection against the are carrying over to the thermal coil,thereby holding volatilization to a minimum.

While the discl9 may be formed of any insulating material, in practisethe most desirable results have been obtained in the use of a materialhaving arc-quenching and deionizing properties. In this respect blackfibre has beeniound to be superior to white fibre, believed to be due toits ability to absorb and retain a greater amount of moisture. v

Inasmuch as the spring I l is spaced and insulated from the link ii,there is no tendency of the link welding itself to the spring uponfusing intermediate its ends, nor of the spring carrying the are alongthe link. A further advantage (112- I termined in insulating the linkfrom the spring resides in the fact that harmless overloads heat thelink II to such an extent that the spring becomes overheated when incontact with the same,

thus affecting its temper to the extent that'its resiliency isdestroyed.

Heretofore, in conventional fuse structures of the type disclosed inFigure 1, it has been customary to merely project the bare fuse linkbetween the telescoping walls of the casing sections,

and under such conditions it has been found that the are frequently hasa tendency to travel the entire length of the link, causing the same toburn and volatilize, all of which creates excessive pressure, whicheither ruptures the casing or creates ignitions, causing the fuse toweld in the fuse holder due to a flash-over.

The foregoing objections have been entirely overcome by the provision ofthe insulating'wrap per H, which surrounds that portion of the fuse linkextending between the telescoping portions of the shell 2 and thimble 3.The wrapping may be of any pliable insulating material, suchas paper,asbestos, or the like. However, it is preferred to use a hygroscopicmaterial, such as paper impregnated with a deionizing ingredient.Satisfactory results have even been obtained with gummed paper, whichhas a tendency to retain a sufflcient amount of moisture to efiectivelycool or quench the are so that portion of the link extending between thesections of the casing will not volatilize.

Inasmuch as a slightly tapered fit is provided between the outer shell 2and the thimble 3, a clamping or wedging action between the twoapparently increases the smothering effect of the insulating wrapper,due to forcing the same into tight, intimate contact with the fusestrip.

In that form of the invention shown in Figure 3, the insulating filler24' likewise serves to smother burning of the link, and prevents thearc,

from discharging or flashing past the casing.

In a cartridge type fuse, such as shown in Fig-- of the link as requiredin plug type From the foregoing explanation, considered in connectionwith the accompanying drawings, it is believed that the advantages ofthe present invention will be apparent, in that the same provides forthe reduction of metal volatilized, thereby reducing the gas pressuresgenerated, as well as the duration of the arc, which, because of theshields provided, is quickly quenched, and prevented from spreading toother parts of the connection between the fuse contacts, all of whichreduces damage to the fuse casing, and the possibility cf fire hazardfrom ignitions and flashovers to a minimum.

Inasmuch as the resilient means provided, instantane usly spaces thesevered portions of the connectic n between the contacts upon fusing,and in so doing raises the disc IS, with the assistance of pressuregenerated within the chamber or compartment 2!, the raised position ofthe disc serves as an indicator of the condition of the fuse. 2

Also, under all conditions of fusing, the link itself is slapped againstthe micawindow by the spring, which affords an additional and plainlyvisiblev indicator.

We claim:

1. A circuit interrupter comprising, a casing of,

insulating material, a pair of terminals carried by the casing, a heatgenerating element of rela-' tively high resistance connected to one ofsaid terminals, a fusible link having one end connected with said heatgenerating element by a low melting point fusible material and itsopposite end connected to the other of said terminals, said link beingof lower resistance than said heat generating element and of greaterresistance thansaid low melting point fusible material and a fibre disclocated on said strip adjacent said thermal element to form a closedcompression chamber within which the thermal element is located.

2. A circuit interrupter comprising, a casing of insulating material, apair of terminals carried by the casing, a fusible link connecting saidterminals, a flat metallic spring positioned under said link andnormally under stress to part the severed portions of said link uponfusing, and heat insulation disposed between said link and sprins- 3. Acircuit interrupter comprising, a casing of insulating material, a pairof terminals carried by the casing, a fusible link connecting saidterminals, a flat metallic spring positioned under said link andnormally under stress to part the severed portions of said link uponfusing, said spring being spaced from said link throughout substantiallythe entire portion of the link disposed within the interior of thecasing and hearing upon the link adjacent its inner end, and insulationdisposed between said link and spring.

4. A circuit interrupter comprising, a casing of insulating material, apair of. terminals carried by the casing, a heat generating elementconcasing and bearing against the link adjacent its connection with saidthermal element, and insulation disposed between said link and spring.

5. A circuit interrupter comprising a casing of insulating material, apair of terminals carried by the casing, a thermal element connected toone of said terminals, a fusible link connecting said thermal elementand the other of said terminals, a fibre disc located on said linkadjacent its connection with said thermal element, said disc forming aclosed compartment within which the thermal element is located, a flatmetallic spring posl tioned under said link and normally under stress topart the link from the thermal element when the link is releasedtherefrom, said spring being spaced from said link throughoutsubstantially that portion of the link disposed within the interior ofthe casing and bearing against the link adjacent said disc, andinsulation disposed between said link and spring.

6. A circuit interrupter comprising, a casing consisting of a pair oftelescoping sections formed of insulating material, a terminal carriedby each of said sections, a thermal element connected to the terminalcarried by the inner section, a fusible link connecting said thermalelement and the other of said terminals, said link extending between thewalls of the telescoping sections, a wrapper formed of pliable sheetinsulating material surrounding thatpart of the link extending betweenthe telescoping sections whereby the wrapper is forced into intimatecontact with the link, a fibre disc located on said link adjacent saidthermal element, and forming a closed compression chamber within whichthe thermal element is located, a flat metallic spring positioned undersaid link and normally under stress to part the link from the thermalelement upon release from the same, said spring being spaced from saidmaterial throughout substantially that portion of the link disposedwithin the interior of the casing, and bearing against the link adjacentsaid disc, and insulation disposed between said link and spring.

7. A circuit interrupter comprising, a casing of insulating material, apair of terminals carried by the casing, a fusible link connecting saidterminals, and a flat metallic spring positioned under said link andnormally under stress to part the severed portions of said link uponfusing.

OSCAR H. JUNG. PAUL E. HEFFEIFIIIGER.

